Displace modifier RGB to XYZ Direction, how to invert on the x axis only
I have solved my issue using nodes rather than a modifier thanks to the suggestion @Allen Simpson commented. I'm fairly new to the workflow and application of shader nodes but I will try to explain in more detail.
My issue was that I needed to turn my texture map into a Vector Displacement node to point my displaced geometry in a consistent direction something the Displace Modifier can also do using the textures RGB values. the only issue is the modifier method requires you to set RGB values in the Texture Properties &gt; Colors &gt; R,G,B and it only accepts values 0-2. you can use the strength value in the Displace Modifier to multiply that value even in the negative direction but it applies it to all 3 RGB values equally. not sure if there is a way to do what what I needed via the modifier but that's ok.
After giving the shader nodes another go I found the Separate RGB node and everything clicked from there. After feeding it my color from my Image Texture nodes output I fed the R value, which represents the only axis I wanted to modify, into a Math node and multiplied by -1 and fed the output and the G and B into their respective X, Y, Z values in a Combine XYZ node. Then I dropped that output into a Vector Displacement node to give the displacement its direction.

With this solution you can easily build a vector by adding a Math node to each of the other values on the Separate RGB node before combining them as XYZ!
Also to answer my own other questions;

Clamp works like Clamp in the Mirror Modifier in that IF there are any values below 0 and Clamp is turned on, it reverts to 0 but it does not automatically grant your colors RGB values to go below 0. No such thing as a negative color value after all. Not sure if there is a way to get the negative values for the Displace modifier but its not that way. Nodes do a good job of letting you take a value from the color and then mod it as you need. Much easier imo.

Not sure but it seems like a harder way to do this, but it would be good for getting a different effect. I think it can make really psychedelic kaleidoscope like geometry animations?